Carbon fiber reinforced composites are known for their outstanding mechanical properties associated with a low density. Some of those outstanding mechanical properties include superior tensile, flexural, and shear properties and impact resistance. For this reason, they have been of interest to many fields, particularly for rugged applications, such as the space and aeronautics industries, military equipment, transportation, and infrastructure.
Carbon fiber-epoxy composites are particularly used in such rugged applications. Although there has been a desire to extend the application of carbon fiber-epoxy composites to more commonplace markets, such as the automotive industry, tools, appliances, and sporting and recreational goods, their extension into these other markets has been substantially impeded by the higher cost of high performance epoxy resins relative to other resin systems. Less costly substitutes of epoxy resin have been sought, but the mechanical properties of these substitutes have thus far not approached the outstanding mechanical properties provided by high performance epoxy resins.
Vinyl ester resins are less costly than high performance epoxy resins, and are widely used, particularly because of their high resistance to moisture absorption and corrosion. Thus, vinyl ester resins would be a highly desirable substitute for an epoxy resin if only the resulting carbon fiber-vinyl ester resin composite could approach the outstanding mechanical properties provided by epoxy resin-based composites. However, the mechanical properties of carbon fiber-vinyl ester composites cannot currently compete with the mechanical properties of carbon fiber-epoxy composites. For this reason, carbon fiber-vinyl ester resin composites have not been considered for applications in which outstanding mechanical properties (e.g., high strength and ruggedness) are required.
The physico-chemical and mechanical properties of a composite material are not only dependent on the characteristics of the reinforcement material and the matrix, but also largely dependent on the properties of the interface. If the fiber-matrix interface is weak, the structural integrity of the composite material will be compromised. Moreover, unlike high performance epoxy resins, and particularly in the case of a vinyl ester resin matrix, a high cure volume shrinkage can further diminish the integrity of the fiber-matrix interface. Thus, methodologies for improving a fiber-matrix interface in an epoxy matrix are generally not applicable for a vinyl ester resin or other type of matrix. For this reason, vinyl ester resin composites have been largely unconsidered for rugged applications, although vinyl ester resins are less costly than high performance epoxy resins. Hence, a great benefit would be provided by a methodology that could significantly strengthen the fiber-matrix interface in composites containing any of a variety of polymeric matrix materials, including vinyl ester resins, unsaturated polyester resins, vinyl addition polymers, and more.